Acute Cellular Rejection -I

Morphologically, acute cellular rejection consists of a mononuclear inflammatory infiltrate that is predominantly a T-cell mediated response directed against the cardiac allograft.  In severe cases, there is also participation of granulocytes in the rejection process.  B cell infiltrates are rarely present in mild rejection. However, a substantial increase in activated B lymphocytes and NK cells are seen in moderate rejection, suggesting their important role as promoters and effectors of cellular rejection.

Grading of acute cellular rejection.
Historically, several methods to assess the histologic grade of rejection have been used by different transplant centers and will not be reviewed here.  In 1990, the ISHLT published a standardized international grading system for the purpose of effectively communicating outcomes in multicenter drug trials and among institutions using different treatment regimens.  This was envisioned as a working formulation (WF1990) which was updated in 2004.  The grades of rejection recognized by the ISHLT are based mainly on the amount of inflammatory infiltrate and the presence of myocyte damage.  The absence of cellular rejection is called grade 0R and and example is shown below. In Grade 0 R there is no evidence of mononuclear (lymphocytes / macrophages) inflammation or myocyte damage.

Grade 1 R (mild, low-grade, acute cellular rejection) shows mild or low-grade rejection in one of two ways: (1) Perivascular and / or interstitial mononuclear cells (lymphocytes / histiocytes) which in general respect myocyte borders, do not encroach on adjacent myocytes, and do not distort the normal architecture . (2) One focus of mononuclear cells with associated myocyte damage may be present .